"I have no way of knowing what the whale had in mind," Richard Ellis, a marine conservationist at the American Museum of Natural History, told The Associated Press. "But I can tell you that killer whales, because they're supposed to be so intelligent, don't do things accidentally. This was not an insane, uncontrollable act. This was premeditated. And the whale, for whatever whale reasons, did this intentionally."

Dolphins have so much brain power that they're thought to rival humans in intelligence. One measure is known as the encephalization quotient, or EQ, which quantifies the size of a species' brain compared with what would be expected based on body size alone.

And dolphins? Species in the dolphin family have EQs ranging from 4 and 5. "This means their brains are significantly larger in relative size than all other animals and second only to modern humans," Marino said.

What's more, the cortex of the dolphin brain is more convoluted than the human cerebral cortex. Thus, on at least one scale of brain function, dolphins beat humans.

Orca intelligence hasn't been studied as intensively as the intelligence of bottlenose dolphins, but orca EQ has been pegged at around 2.5. Toni Frohoff, research director at TerraMar Research, is confident that orcas are not dumb animals. "If anything, since orcas are the largest member of the dolphin family, their intelligence is perhaps superior to other dolphins," she told me.

Marine mammal's motive?Frohoff suggested that Tilikum, the orca who was involved in the death of trainer Dawn Brancheau at the SeaWorld aquarium in Orlando, Fla., may have been suffering from the cetacean equivalent of anxiety disorder.

"We know that post-traumatic stress syndrome has been identified in other species, by [animal specialist] Temple Grandin and others," Frohoff said. "PTSD is very possibly related to his action. The act of capture alone, let alone the sustained and chronic stress that he is subjected to, could easily be responsible for that. ... He's been trying to communicate, and nobody's been listening."

Researchers generally say that confinement in a holding pen for long periods of a time is stressful for marine mammals, which typically swim 75 to 100 miles a day in the wild.

Tilikum was a special case for several reasons: He's the largest orca in captivity, weighing in at more than 6 tons. In confinement, he'd feel especially pinched by his goldfish-bowl surroundings. He was separated from his Icelandic family pod at the age of 2. That would be particularly stressful for a species so tied to family life that each pod has its own dialect of calls. And because he was involved in two earlier human deaths, in 1991 and 1999, Tilikum was even more isolated than the typical captive orca.

Some might wonder why Tilikum was still at SeaWorld after those earlier deaths. "Because of the previous incidents, he has been kept in isolation most of the time - except for breeding," Susan Berta, co-founder of the Orca Network in Washington state, told me. "That's why he was kept on. He's sired 17 calves."

"He isn't a bad seed or a serial killer," Marino told me in an e-mail. "He is an intelligent sensitive animal taken from his family when he was 2 years old and forced to lead a highly artificial and confined life. This tragedy is just one example of what happens when we continue to use animals in this way. It is also critical to note that there has not been a single documented case of an orca injuring a person in the wild. People do swim with them or get among them in very small inflatables and boats, and there has yet to be an incident. All of these terrible events occur in captivity."

What to do with a killerMarino worried that Brancheau's death may lead SeaWorld to give Tilikum what would amount to a lifelong sentence in solitary confinement. "That would be the worst thing that could happen to this whale," she said. "That really could worsen the situation."

She and many of her colleagues in the marine science community say that captivity isn't healthy for orcas, or for studying them scientifically. "There is a good deal of information from the orcas, but most of it has come from the wild," said Diana Reiss, a cognitive psychologist at Hunter College in New York.

During the AAAS meeting, Reiss, Marino and other scientists called for a halt to practices such as dolphin drive hunting and the capture of dolphins, including orcas. One ethicist, Thomas White of Loyola Marymount University, said the mammals' behavior and neurophysiology suggested that they had "all of the traits that philosophers traditionally require for persons." (A similar debate over personhood has been percolating over the status of chimps.)

Ellis said this week's incident would likely have the ironic effect of raising the popularity of marine mammal shows like the ones at SeaWorld. But Marino said the Tilikum tragedy should instead spark a reassessment of the sea's most intelligent species.

Marino suggested that Tilikum and other captive orcas could be rehabilitated to return to the wild, or at least go to marine sanctuaries (like the one that sheltered Keiko, a.k.a. the "Free Willy" whale). The Orca Network is currently campaigning for the release of Lolita, a performer at the Miami Seaquarium that is the only member of the Southern Resident orca population still held in captivity.

"We need to have a conversation about whether these animals should be entertaining us in these tanks," Marino told me.

So let's converse: Before you start thinking about orcas as if they were plush toys, check out this commentary from Georgetown University biologist Janet Mann. "We forget that they are called killer whales for a reason and there is nothing warm and cuddly about that," she writes.

The idea of marine mammals striking back has had such a hold on the human psyche that it's been satirized by The Onion and "The Simpsons." As we get to know other species better, will our attitudes toward them change? Or was this tragedy brought on by a rogue killer, pure and simple? If orcas really are intelligent persons, shouldn't they be held liable for what they do? Feel free to weigh in with your comments below.

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